Binge alcohol drinking is practiced by an estimated 38 million adults in the United States and factors into more than 50 different injuries or diseases including burn injury. Clinical evidence reveals that 50% of burn patients are under the influence of alcohol at the time of hospital admission and that the combined insult of alcohol and burn injury causes increased risk of pulmonary complications leading to multiple organ failure and death. Our previous work demonstrated that in a mouse model binge ethanol followed by a moderate size burn injury there was prolonged pulmonary inflammation characterized by amplified neutrophil accumulation, dramatically increased pro-inflammatory cytokine IL-6 levels, and decreased anti-inflammatory IL-10 levels, relative to either ethanol exposure or burn injury alone. Successfully controlling this excessive pulmonary inflammatory response is essential to reducing morbidity and mortality rates in patients with combined injury. The anti- inflammatory benefits of mesenchymal stem cells (MSCs), including endogenous distal lung MSCs, have become a prominent area of interest as a means of attenuating inflammation. MSCs have been characterized as potential modulators of acute inflammation by virtue of their ability to recruit innate immune cells to the site of injury and modulate the phenotype of those cells to an anti-inflammatory profile. MSCs direct contact with macrophages or the release of paracrine factors by MSCs has been shown to trigger macrophages into an anti-inflammatory M2 phenotype, resulting in the amplified release of anti-inflammatory cytokine IL-10. Alveolar macrophages play a critical role in both the initiation and the resolution of pulmonary inflammation. The location o distal lung MSCs and alveolar macrophages in the pulmonary interstitium justifies an investigation into whether ethanol disrupts communication between these two cells types. We hypothesize that ethanol exposure prior to burn injury reduces the frequency and/or function of endogenous lung MSCs, and that this disruption results in excessive pulmonary inflammation. Furthermore, the local inflammation remains elevated because anti-inflammatory mediators derived from lung MSCs are not present and thus cannot initiate a shift of alveolar macrophage from M1 to M2 phenotype. Aim 1 will determine the effect of ethanol prior to burn injury on the frequency, distribution and function of lung MSCs and alveolar macrophage populations. Aim 2 will elucidate mechanisms by which ethanol decreases the ability of lung MSCs to reprogram macrophages from a M1 to a M2 phenotype and whether isolated lung MSCs expanded in culture can be used as a post-injury therapy to reduce pulmonary inflammation. This proposal will identify whether ethanol alters the frequency or function of cellular subsets in the lung miliu and, at the completion of the proposed research, we anticipate identifying novel local therapeutic targets which will help to improve survival in all burn patients.